Feeding by Northern Brook Lamprey ( Ichthyomyzon fossor ) on Sestonic Biofilm Fragments: Habitat Selection Results in Ingestion of a Higher Quality Diet

This study examined interrelationships among habitat type, selective feeding, diet quality, assimilation efficiency, and condition in larval northern brook lamprey ( Ichthyomyzon fossor ) in three lower order streams in Michigan's Upper Peninsula. Larvae were less abundant in sand (site means = 0.2 to 0.5 larvae / 2,500 cm 2 ) than in organic sediment (0.5 to 2.85 / 2,500 cm 2 ). Within patches of organic sediment, larvae aggregated at sites where obstacles to flow caused localized accumulation of flocculent material (≤ 26 larvae / 2,500 cm 2 ). Ingestion was selective, with both amino acid and total organic matter higher in foreguts than in seston. Habitat type selected by a larva had relatively minor consequences for organic matter and amino acids in the diet, but had major consequences for assimilation efficiency for both nutrients with highest efficiencies in depositional areas where larvae aggregated. Condition factors (weight per length) were similarly highest in these depositional areas. Variation in diet composition over time suggests an annual cycle of seston production resulting from biofilm sloughing from solid surfaces as controlled by stream discharge and the availability of light to support algal production.